A new study claims that children who spend long hours in daycare are more likely to have temper tantrums, dummy-spits, and a worse case of the "terrible-two's".

The study of more than 5000 toddlers showed that those who spend more than 20 hours a week in childcare experience the equivalent of an 11-month developmental delay. However, it also found that these children are more sociable and outgoing with strangers.

Research co-author Dr Andrew Leigh, said the findings may not be too surprising, but in any case, should not worry parents.

"We did find that the terrible-two's are more terrible for kids in non-parental care, but it's a stage all children go through.

"The kids in daycare seem to be very slightly worse off in outcomes, but the effect is pretty small, and we shouldn't think about childcare having one effect on all kids."